Siphonorhinidae

Cook, 1895

Siphonorhinidae is a of in the Siphonophorida, characterized by super-elongated trunks with more than 180 diplosegments and leg counts exceeding 710 in some . The family includes the leggiest animal on Earth, Illacme plenipes, with females possessing up to 750 legs. Members are small, threadlike, slow-moving, unpigmented, and inhabit deep soil microhabitats. The family exhibits a fragmentary, disjunct distribution across California, southern Africa, Madagascar, the Malay Archipelago, Indo-Burma, and now Chile. Siphonorhinidae is represented in the Western Hemisphere solely by the Illacme in California and the newly described genus Notorhinus in Chile.

Siphonorhinidae by (c) Marek, P.; Shear, W.; Bond, J. (2012), some rights reserved (CC BY). Used under a CC-BY license.

Pronunciation

How to pronounce Siphonorhinidae: /sɪfənoʊˈrɪnɪdi/

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Identification

Distinguished from other by extreme leg count (highest in Animalia), threadlike unpigmented body, and deep soil . Diagnostic features include pear-shaped and , though these may need critical reexamination based on recent phylogenomic analyses. Distinguished from the related family Siphonophoridae by somatic and sexual characters; Siphonorhinidae is with respect to Siphonophoridae. The Notorhinus is distinguished from other Siphonorhinidae by arrangement of on .

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Habitat

Deep soil microhabitats; endogean (subterranean) lifestyle. Found beneath stones, decaying oak logs, and within soil matrix at depths of approximately 3 cm. Oak woodland in California; degraded central highland rainforests in Madagascar; fragmented forest in Chile; areas with thick fog accumulation, sandstone boulders, and fine sandy soil.

Distribution

Fragmentary, disjunct distribution: California (USA), southern Africa, Madagascar, Malay Archipelago, Indo-Burma, and Chile. Western Hemisphere representation limited to California (37°N) and Chile (38°S), showing antitropical disjunction. Closest relatives separated by since Pangaea more than 200 million years ago.

Life Cycle

Euanamorphosis: individuals emerge from with at least four leg pairs and incrementally add legged- during development, continuing even after sexual maturity. Some reach 182–330 rings through this ongoing segment addition.

Behavior

Very slow ; burrows through soil using concertina-like fashion. Movement facilitated by compressible due to primitively unfused , extensible and flexible body, continuous metachronal wave gait, and action of concentric tubular rings sliding within one another. Longitudinal and oblique muscles pull rings together to facilitate forward locomotion.

Human Relevance

Subject of scientific interest due to holding record for most legs of any animal; Illacme socal discovered in Los Angeles metropolitan area highlights concern for subterranean fauna threatened by urban development. Discovery of new emphasizes importance of preservation to prevent anonymous extinction.

Similar Taxa

SiphonophoridaeOther in Siphonophorida; Siphonorhinidae is with respect to this family based on phylogenomic analyses. Distinguished by somatic and sexual characters.
PolyxenidaAnother with elongated bodies, but with distinct including bristle-like and different preferences.

More Details

Phylogenetic Note

Siphonorhinidae is with respect to Siphonophoridae based on phylogenomic analysis from Marek et al. (2021), suggesting -level based on may need critical reexamination.

Conservation Concern

Subterranean fauna including Siphonorhinidae are grossly understudied and threatened by encroaching human settlement and loss. of these is of high importance.

Evolutionary Significance

The antitropical distribution pattern in the Americas (California and Chile) suggests these may be relicts of a once greater distribution that persisted due to similar climatic conditions, with relationships established more than 200 million years ago during Pangaea.